Dnkldorf—some interesting questions… If I follow your explanation, aside from medium-voltage distribution, there is a 480V corner-grounded system, a 240V corner-grounded system, and a 208Y/120V system essentially “under one roof.”
All have grounded-circuit conductors, but the only true neutral is in the 208Y/120 system—for it carries unbalanced current in multiwire feeders and branch circuits, where the “white wires” in the 480 and 240 systems do not.
About overcurrent protection in grounded-circuit conductors—in the case of running-overload protection in three-phase motors—there must be overcurrent-protective devices in each of three phase conductors—ungrounded or grounded. For this reason, if time-delay fuses are used for motor running-overload protection, then a fuse is required in the grounded-circuit conductor of each motor branch circuit—which is indeed a “white wire.’
On the 208-to-480V “bleed” problem, the only way that could happen would be to use a remote 480V grounded-circuit conductor as the ground electrode for which of the 208Y/120V-transformer XO terminals—which would be unlikely to occur intentionally or accidentally.
